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I was playing MTG with some friends the other day, when a guy walks up and challenges me to a game. He insisted that he would not roll my spin-down die to determine who goes first. When I pointed out that it doesn't matter, because probabilistically, each side should have a 1/20 chance of showing regardless of the order of the sides, he assured me that there exists a "technique" by which someone could throw an ordered dice such that he has a higher chance to win a dice roll.

Paranoia aside, does anyone know if such a technique exists? Is there any documentation on such a technique?

I believe it's known as a "controlled shot" in gambling. It's the reason you're required to throw your dice against the wall in craps. Having all the high numbers on one side makes it much easier.
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Alex PJun 1 '12 at 17:22

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One fairly obvious way to cheat with a die (that I've seen used) is to spin the die rather than rolling it. For a standard six sided die in particular this makes it easy to aim for 4/5/6.
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tttpppJun 1 '12 at 17:23

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The standard way I've seen of doing this with spindowns is the 'drop roll', where rather than tumbling the die is sort of skittered along the table surface; it won't necessarily land with a specific face up so you can't 'call shots', but if it's thrown with the 'high' side up then the odds of achieving a higher-than-average roll go up substantially.
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Steven StadnickiJun 1 '12 at 17:33

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Love how your opponent was really worried that someone might cheat him and get to play first! What a total rip-off that would be :p
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rahzarkJun 1 '12 at 18:27

5 Answers
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As I noted in a comment, there are techniques I've seen people use with spindown dice - most notably a sort of 'skitter along the table' throw where the die is primarily slid rather than tumbled - that can be used to great effect in rolling high numbers. There's enough imprecision that shots can't really be called precisely, but for spindown dice where all of the faces around a high-numbered face are also high-numbered, they lead to significantly biased rolls.

You might ask why it matters, since both players are rolling the same die and both have access to the same technique - but the point is that there's an ethical asymmetry; one player is (presumably) trying to roll the die in a 'fair' fashion with an unbiased roll, either out of a sense of internal fairness or because they have no reason to suspect the other player is cheating them. Meanwhile the shark is (also presumably) well aware of the skew in the game and willing to use that skew to his advantage.

For what it's worth, I don't believe most people rolling spindown dice do it with any intention to cheat; the life counter is just what they have handy, and so it's a natural choice. But there are people who will use it for that purpose, and so anyone who isn't willing to is at a slight overall disadvantage. Most of the time, at an FNM or in a casual game like the one you describe, it just doesn't matter; who cares if you're an underdog in a die roll that has a maybe 5% affect on the outcome of a game that's just for fun? But there are certainly circumstances where it does matter, and some people just get in the habit of caring about every little thing so that they build the mental rigor for when it does matter.

As for myself, I usually don't care, though at something like a PTQ I'll insist on a more effective means of randomization. My preferred choice is either to flip a coin with a call in the air (which is about as close to 'I cut, you choose' as a randomization method gets) or to toss about 5d6; they're quick enough to count, and hard enough to really skew that I can trust in the results.

Still using the die, one person rolling and the other calling odd or even is an easy method.
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GregorJun 1 '12 at 19:51

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Is there any documentation at all for these techniques? Maybe something like a video, or someone doing a "magic trick" or something like that? I'm not sure I can visualize how this would turn out. I find it somewhat difficult to believe that someone could roll a die so that there's a higher chance that half of it would show up without it appearing super obvious that they're doing so.
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TeofrostusJun 2 '12 at 0:08

Who goes first has a significantly higher effect than just 5% on the game
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HyppyJun 13 '12 at 14:10

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the impact of going first varies significantly based on format, for larger formats (Vintage, legacy, modern) I would agree that it may very well be more than 5% (with some decks, particularly combo decks), however smaller formats like standard the impact is reduced. In general the lower the fundamental turn, the more important going first is.
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PattersNov 25 '13 at 9:27

Certainly there are tricks to rolling dice, but I believe all but one of them apply to a D6 at best. The more numbers your die shows, the harder any trick becomes, because a D20 topples much more easier than a D6, because its ratio of weight per single face area is much larger than for a D6, and the angles between faces are much larger than 90°. Compared to a D6, a D20 is practically a ball. A D20 simply cannot hold virtually ANY momentum with a single face, unlike a D6.

Try painting a small spot on a marble and make it land on exactly that spot. There is pretty much only 1 somewhat reliable way to do it: Spinning the marble on the spot and hoping that it doesn't spin out of control in the end. That's the only trick I can imagine could work for a D20. Fortunately, that trick is trivial to spot, so as long as someone does a normal rolling motion, a D20 should be safe from manipulation.

All that is assuming fair dice - if someone wants to retreat to the position that your die is physically manipulated, you can't disprove that any way short of cutting up your die.

With a spindown, though, the dot on the marble is effectively more like a hemisphere.
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Alex PJun 1 '12 at 17:50

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If the goal is to throw a specific number, this is true - but if the goal is to end the roll with some face just in the vicinity of 'up' instead of at the top, then there are still techniques that work just fine for D20s. And that's why the fact that the die is spindown matters; unlike a 'random' D20 where the numbers are evenly distributed across the die, on a spindown just getting close enough really is good enough.
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Steven StadnickiJun 1 '12 at 17:50

This controlled die rolling stuff is just nonsense... its simply a meaningless factoid that ego-inflated magic players use on each other to try and build themselves up before a game.

Yes, spindown dice do not have evenly distributed numbers, but if you are telling me someone can casually pick one up and control their roll to be better than mine then you are delirious. To achieve this you'd have to pick up the die, find the high/low side, and then carefully roll/drop it to get the desired result. By this time you are looking at the guy like "are you kidding me man... you are trying to cheat the roll!"

People will relish the rare attempts they get to demand the 2d6 roll, and they will spout this reason every time with a proud smile on their face, now sure that they know all the ins and out of magic better than you do.

I suggest you smirk to yourself at what a tool they are and roll whatever they want... then crush them in the game!

"To achieve this you'd have to pick up the die, find the high/low side, and then carefully roll/drop it to get the desired result." - Unless you already know where the high and low sides are, because it's already been sitting right there on the table in sight and you put it down with the '20' on top anyway (which is pretty reasonable to do).
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doppelgreenerJul 31 '14 at 23:45

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The kind of person who wants to cheat is going to try to practice it enough to get away with it, not just come out and do something crazy right in front of you.
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JefromiAug 1 '14 at 6:33